1. Field of the Invention
This invention relates, generally, to syringes. More particularly, it relates to a syringe where the position of the plunger is controlled from a point near the leading end of the syringe.
2. Description of the Prior Art
A conventional syringe structure includes a needle held at its base by a hub that is mounted at the leading end of a barrel. A plunger is slideably mounted in the barrel, and a piston having annular seals is provided at the leading end of the plunger. In a syringe intended to be used as an aspirator, withdrawal of the piston/plunger in a leading-to-trailing direction creates a vacuum in the leading end of the barrel that pulls liquid fluid into the barrel. In a syringe intended to be used for injection, displacement of the piston/plunger in a trailing-to-leading direction drives a liquid fluid out of the barrel and through the needle into the patient""s tissue.
Some syringes are used for aspiration and injection. Thus, the plunger is retracted to accomplish aspiration, and thereafter advanced to accomplish injection. When a conventional syringe is used in this manner, the physician must develop a technique whereby the needle remains properly positioned during the retraction and the advancement of the plunger. The most common way of performing an aspiration is for the operator to hold the barrel in a first hand and to retract the piston/plunger with a second hand. For injection, the operator usually employs a one-handed technique. The operator steadies the barrel by holding two laterally-extending tabs at the trailing end of the barrel with the index and middle fingers and by using the thumb to advance the plunger in a distal-to-proximal (trailing-to-leading) direction in a well-known way.
There are occasions, however, when it is necessary to inject substances in a precise location, such as a vascular space. Any inadvertent injection of the substance outside its intended target may harm the patient. For example, in the practice of sclerotherapy, a caustic substance is injected into superficial, diseased veins to destroy them. The veins may be quite small and thin-walled and they are typically difficult to calculate precisely with a needle tip. The patient experiences tissue destruction, ulceration and the pain concomitant therewith if the caustic substance is injected into tissue adjacent the diseased vein, so precision injection is a necessity. Accordingly, when performing an intravascular injection, the physician confirms needle tip location in the vascular space by aspiration until blood is seen. This requires retraction of the plunger. Injection, which requires advancement of the plunger, may then proceed.
The syringes now in use require the physician to change hand positions between the aspiration and the injection. Most physicians have developed their own personal techniques for controlling the plunger position with the same hand that holds the barrel of the syringe. These techniques include positioning a little finger on the trailing end of the plunger, holding the barrel in the palm of a hand so that the palm controls the plunger position, and other non-ergonomic techniques. The drawback of these techniques is that they require a high level of skill and cannot be repeated with consistency. Moreover, a change in hand position can lead to an accidental extravascular injection.
A number of syringes suitable for one-handed operation have been patented, but many of them are relatively complex in construction, difficult to use, and expensive to manufacture.
What is needed, then, is a syringe of the type that facilitates one-handed control during aspiration and injection. The improved syringe should reduce the level of skill required for its use. Moreover, it should have a simple construction, be easy to use, and should be economical to manufacture.
More particularly, a syringe is needed that enables sequential aspiration and injection with one hand in the absence of any need to change hand positions or to otherwise place the fingers, thumb or palm in an awkward position. The ideal syringe would enable the operator to control the instantaneous position of the plunger with a single digit such as a thumb or a finger without requiring movement of any other part of the hand. This would provide more stability so that accurate injection into the proper space could be accomplished. The control point should be positioned forwardly, near the needle, to facilitate its use.
However, it was not obvious to those of ordinary skill in this art how the needed syringe could be provided, in view of the art considered as a whole at the time the present invention was made.
The long-standing but heretofore unfulfilled need for an innovation that overcomes the limitations of the prior art is now met by a new, useful, and nonobvious invention. The novel syringe of this invention is adapted to be held in a single hand. The operator of the syringe can perform aspiration and injection in sequence without changing hand position. The syringe construction includes a needle, a hub for holding the needle, a barrel having a leading end to which the hub is mounted, an elongate plunger having a leading end slideably mounted within the barrel and a trailing end that is external to the barrel, and a slide member that slideably engages an external surface of the barrel. A yoking means interconnects the slide member to the trailing end of the plunger. The slide member is adapted to be controlled by a thumb or finger of a user so that manipulation of the slide member controls an instantaneous position of the plunger.
The slide member is positioned at a leading end of the barrel, in closely spaced trailing relation to the leading end of the plunger so that the syringe operator can easily observe the respective positions of the slide member and the forward end of the plunger at the same time.
The slide member includes a first part for slideably engaging the barrel and a second part adapted for abutting engagement by a thumb or finger. The first part conforms to a curvature of the barrel and the second part is relatively flat to provide an ergonomic support surface for a thumb or finger.
The first part may encircle the barrel, having an inner diameter slightly greater than an outer diameter of said barrel.
Alternatively, the first part may be arcuate in configuration and extend more than one hundred eighty degrees in circumference around the barrel so that the barrel is slideably captured therewithin.
The yoking means includes an elongate rod disposed in substantially parallel relation to the plunger and interconnecting means for connecting the elongate rod to the plunger. The elongate rod has a leading end secured to the slide member and a trailing end connected to the trailing end of the plunger.
A guide means is mounted to a trailing end of the barrel for maintaining the elongate rod in substantially parallel relation to the plunger. The guide means is provided in the form of an apertured or slotted tab mounted at the trailing end of the barrel; the aperture or slot slideably receives the elongate rod.
The interconnecting means includes a first transversely disposed flange secured to the trailing end of the elongate rod and a second transversely disposed flange secured to the trailing end of the plunger. The flanges have a diameter sufficient to cause them to abut one another, and an adhesive means is provided to secure the flanges to one another.
The interconnecting means alternatively includes a flat plate adhesively secured to respective trailing ends of the elongate rod and plunger.
In another embodiment, the interconnecting means includes a return bend that interconnects respective trailing ends of the elongate rod and plunger.
A plurality of longitudinally spaced apart, radial projections may also be mounted along the extent of the barrel to provide finger-receiving spaces therebetween. These projections keep the fingers and hand from moving relative to the syringe during operation of the syringe.
It is a primary object of this invention to provide a syringe for performing one-handed aspiration and injection in sequence in the absence of any need to reposition the hand at any time.
Another object is to provide a syringe structure having means mounted externally of the syringe barrel for controlling an instantaneous position of the plunger.
These and other important objects, features, and advantages of the invention will become apparent as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.